Process for the preparation of pentaerythritol

Abstract

A process for the preparation of pentaerythritol, comprising reacting formaldehyde, acetaldehyde and sodium hydroxide and acidification with formic acid. These steps take place in a reactor with supplies of formaldehyde, sodium hydroxide, acetaldehyde and formic acid and at the end the solution formed is evacuated to a buffer tank of larger capacity than the reactor. In the reactor new reactions and acidifications are successively reinitiated by new supplies. In the first place a formaldehyde solution is added, followed by simultaneous but separate additions of sodium hydroxide solution and acetaldehyde, forming a reaction mixture in such a way that the flowrates of the solutions vary with the time and that the temperature at which the reactions are conducted also varies with the time. The outflow from the buffer tank is constant and continuous.

What I claim is: 
     
       1. A process for the preparation of pentaerythritol, comprising the initial steps of:  a! reacting formaldehyde with acetaldehyde, to give pentaerythritose; and subsequent reaction of said pentaerythritose with formaldehyde and sodium hydroxide, to give a solution containing pentaerythritol; and  b! acidification of said pentaerythritol-containing solution with formic acid; said steps  a! and  b! being conducted in a reactor, with the supply of formaldehyde (CH 2  O), sodium hydroxide (NaOH), acetaldehyde (AcH) and formic acid (HCOOH) and at the end of said steps the formed pentaerythritol-containing solution being drained to a buffer tank of a capacity greater than that of the reactor, new reactions and a new acidification operation being successively reinitiated in said reactor by fresh supplies, wherein, in the first place, a formaldehyde solution and thereafter, simultaneously but separately, sodium hydroxide solution and acetaldehyde are supplied, forming a reaction mixture and because the exit flow from the said buffer tank is substantially constant and continuous. 
     
     
       2. The process of claim 1, wherein the sodium hydroxide is added gradually such that the pH of said reaction mixture is held between 10 and 11, and throughout the addition the temperature and the acetaldehyde flowrate vary. 
     
     
       3. The process of claim 1, wherein at least one of the sodium hydroxide supply and acetaldehyde supply flowrates undergoes at least one variation. 
     
     
       4. The process of claim 3, wherein the variation of each of said flowrates takes place substantially continuously. 
     
     
       5. The process of claim 3, wherein the variation of each of said flowrates determines at least two periods of different flowrates, the flowrates being held substantially constant during each of said periods. 
     
     
       6. The process of claim 1, wherein said reactions are conducted at a variable temperature. 
     
     
       7. The process of claim 6, wherein said variability is substantially continuous. 
     
     
       8. The process of claim 6, wherein said variability determines at least two periods of different temperatures. 
     
     
       9. The process of claim 7, wherein at the start of said reactions the temperature is held within the range of 20° to 38° C., while at the end of said reactions the temperature is held within the range of 42° to 48° C. 
     
     
       10. The process of claim 1, wherein the concentration of said formaldehyde solution is in the range of 20 to 30 wt %, the concentration of said sodium hydroxide solution is in the range of 12 to 20 wt % and said acetaldehyde is substantially pure and the molar proportions CH 2  O/NaOH/AcH are in the range of 5.1-9.5/1.05-1.4/1.0. 
     
     
       11. The process of claim 1, wherein the successive supplies to said reactor comprise: a first period in which substantially half of the volumes is supplied, the temperature being held within the range of 22° to 28° C.; a second period in which substantially one fourth part of the volumes is supplied, the temperature being held within the range of 32° to 38° C., the duration of said second period being substantially the same as that of the first period; and a third period in which the supplies to the reactor are completed, the temperature being held within the range of 42° to 48°, the duration of said third period being greater than that of the second period.